The present invention relates to a recycling process for the recovery of organic solvent used, for example, in the dry cleaning industry. More particularly, it relates to a solvent recovery and purification process which enables reuse of contaminated solvent.
Solvents are used in a wide variety of applications. Tetrachloroethylene, or "perchloroethylene" or "perc", as it is commonly named, is known to be effective and is thus widely used as a dry-cleaning solvent. In addition to the use of perc, dry cleaners may employ other halohydrocarbon liquids such as for example trichlorofluoromethane, trichlorofluoroethylene, 1-1-1 trichloroethane or the like to remove a mixture of fatty acids, hydrocarbon-based oils, oil-soluble and insoluble dirt and soil, water and aqueous body moisture, from garments and other fabric products.
In the common dry-cleaning process, soiled garments and other fabrics are loaded for cleaning in hot agitated wash tanks. A volume of organic solvent is continuously recirculated from a contacting zone comprising agitated wash tanks, processed through filter equipment and returned to the wash tanks. One of two filter types are typically employed. The first type of filter uses fabric bags coated with filter aids such as diatomaceous earth, carbon black, surfactants, and the-like, through which the soiled solvent is passed.
The other common filter process employs disposable filter cartridges. Such cartridges typically comprise cellulose and activated carbon which retain a portion of the various contaminants and allowing the return of filtered solvent to the contacting zone. As may be expected, a portion of organic solvent also is adsorbed into the filter media.
During the use of the filters in the typical dry-cleaning process, the flowing fluid pressure drop across the filter is usually monitored and when the pressure drop rises to a critical level, the filter is generally cleaned or replaced. At this point, the dry-cleaners are faced with a significant problem with respect to the replaced, or "spent" solvent filter cartridges.
Unfortunately, the organic solvents used in the dry-cleaning process, being chlorinated hydrocarbons, have serious disposal problems associated with their use. Moreover, the solvents retained in the filter media are classified as Hazardous Waste under the Resource Conservation and Recovery Act, a federal environmental statute. Therefore, the filter cartridges comprising perchloroethylene and other contaminants may not lawfully be disposed of in common landfills and the like.
Previous workers have attempted to modify dry-cleaning equipment to include solvent recovery processes. In an attempt to solve the continuing problem of contaminated filter cartridges, others have suggested a continuous steam distillation unit as part of the dry-cleaner's equipment.
Another approach to the problem of spent filter cartridges, where filters are employed at the dry-cleaner site, involves collection of the solvent contaminated filter cartridges from the cleaners, and transporting the collected cartridges to a treatment site. A partial solvent extraction is performed, followed by destruction of the cartridge usually by grinding the entire cartridge. However, even when such solvent removal is attempted prior to grinding the filter cartridge, enough solvent typically remains in the filter media at a concentration prohibiting recycle of the filter media for other more valuable uses.
Another major problem with respect to recycling of halohydrocarbon solvents in the dry cleaning industry .involves the accumulation of dissolved compounds in the solvent itself. Contaminants such as for example fatty-acids and lipids are found in the perchloroethylene solvent following its use in dry-cleaning. High odor level is therefore often associated with used perchloroethylene solvent. This is especially true for that partially extracted as explained above. High odor level, combined with high contaminant levels, prohibits the reuse or resale of this perchloroethylene solvent mixture to the dry-cleaning industry.
Used solvent mixtures containing such contaminants not being resalable, are relegated to lower level uses, such as industrial cleaning solvents. Unfortunately, use as an industrial cleaning solvent does not remove or reduce the quantity potentially environmentally harmful compounds from the industrial waste stream. Moreover, since the mixtures were not recyclable prior to the present invention, additional virgin perchloroethylene was required to be manufactured for use in the dry-cleaning operations of interest.
It is apparent that a process for recovery of solvents, which process provides for effective recycling of the solvent, is much desired in the industry.